Global Potential Evapotranspiration Estimation And Change Attribution Analysis Based On The Shuttleworth Wallace “dual Source” Mode

As the theoretical upper bound of evapotranspiration（ET）or water use by ecosystems,potential ET（PET）has always been widely used as a key variable linking a variety of disciplines,such as climatology,ecology,hydrology,and agronomy.However,substantial uncertainties exist in the current PET methods（e.g.,empiric models and single-layer models）and datasets,because of unrealistic configurations of land surface and unreasonable parameterizations.Therefore,based on observed global vorticity（EC）flux data,this study re-parameterizes the Shuttleworth Wallace"dual source"model according to vegetation type,and based on the parameterized model and four sets of meteorological data（namely MSWX-Past,MERRA-2,ERA5,CRU）,a global monthly SWPET product of 5km（1982-2015）is generated.Finally,the temporal and spatial variation characteristics of PET and its two components（i.e.,potential vegetation transpiration PT and potential soil evaporation PE）were analyzed in detail.Six influencing factors（CO₂,LAI,net radiation,relative humidity,temperature and wind speed）were selected to conduct attribution analysis on the changing trends of PET,PT and PE in the world.The main conclusions are as follows:（1）The parameterized SW"dual source"model can simulate different types of LULC PET better,mainly showing small error and high accuracy,more importantly,parameters are spatially portable.（2）On a global average,the multi-year average is 1200mm PET,40%PT/PET and 60%PE/PET;PT（PE）was greater than PE（PT）in 43%（57%）of regions,respectively.In the past34 years,the global average annual PET and PT showed a significant（p<0.05）increase trend,with rates of 1.25mm/yr and 1.22mm/yr,respectively,while the annual PE showed a weak and insignificant increase trend.Globally,>53%（<47%）of regions showed that changes in PET were attributable to changes in PT（PE）.The new PET dataset is expected to be used by academics and various institutions for climate analysis,hydrological modelling,drought research,agricultural water management and biodiversity conservation.（3）Overall,changes in temperature,LAI and CO₂ are the main causes of global changes in PET and its two components.The main reasons for the increase of global PET are the increase of temperature and LAI,while the increase of CO₂ concentration tends to reduce PET.Net radiation,relative humidity and wind speed have certain effects on PET changes,but relatively small.For the two components of PET（PT and PE）,the contribution trends of LAI and CO₂were opposite.Spatially,temperature and LAI dominated 80%,82%（not considering non-vegetated areas）and 88%of the global PET,PT and PE trends,respectively.